Caries, which is a typical example of oral bacterial diseases, is one of two major dental diseases together with a periodontal disease and is a loss of tooth structure caused by erosion (demineralization) of the minerals forming enamel or dentin with acids, such as lactic acid, generated by caries-causing bacteria proliferated on the surface of tooth structure.
In the process of developing caries, a biofilm is formed on the surface of tooth structure. The formation of the biofilm on the surface of tooth structure demineralizes the tooth structure just below the biofilm, leading to caries.
Accordingly, in order to prevent caries, for example, caries-causing bacteria are prevented from proliferating or are sterilized; the biofilm is removed with mechanical means; or the demineralized tooth structure is remineralized.
Among these methods, the proliferation inhibition or sterilization of caries-causing bacteria does not need any special device in its application and is broadly applied. A typical example thereof is gargling with an oral rinse containing a caries-causing bacterium proliferation-inhibiting or sterilizing component. These methods inhibit proliferation of caries-causing bacteria on the surface of tooth structure to prevent the tooth structure from being demineralized, leading to effective prevention of caries.
In particular, a hypochlorous acid solution, which can be prepared by electrolysis of an aqueous solution of a chloride such as sodium chloride, has a high bactericidal effect and is thereby proposed to be used as a liquid mouthwash for dental treatment (Patent Literatures 1 to 4).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. H09-183706    Patent Document 2: Japanese Unexamined Patent Application, Publication No. H10-087462    Patent Document 3: PCT International Publication No. WO2007/072697    Patent Document 4: PCT International Publication No. WO2009/098870